The present embodiments relate to a local coil for magnetic resonance applications,
Images with a high signal-to-noise ratio (SNR) may be recorded in magnetic resonance imaging using local coils. Local coils are antenna systems that are provided in the immediate vicinity on top of (anterior) or underneath (posterior) the object to be examined (frequently a patient). During the magnetic resonance measurement, the nuclei excited to form magnetic resonances induce a voltage in the individual antennae of the local coil. The induced voltage is amplified by a low noise amplifier (LNA) and forwarded to a receiving electronic device. To improve the signal-to-noise ratio in high resolution images, high field units that have a base magnetic field of 1.5 Tesla and above and sometimes even above 12 Tesla may be used.
One measure for improving the SNR lies in arranging the receiving antennae as close as possible to the object to be examined. In some cases, the SNR may also be increased by reducing the size of the receiving antenna (optimized loop diameter). This is very helpful, for example, for applications in which tissue close to the surface is being examined.
In the prior art, the received magnetic resonance signal may be transmitted to a control and evaluation device of the magnetic resonance system via wires. The wired transmission is regarded as being disadvantageous. The reasons for this include, for example, the time required for handling the cables, inserting the connectors, the costs required for the connectors and cables, and patient safety (e.g., sheath waves).
The received magnetic resonance signals are converted to a different frequency and transmitted wirelessly by way of a radio link to the control and evaluation device.
In research in the field of magnetic resonance systems, efforts are currently being made to digitize the magnetic resonance signal before transmitting the magnetic resonance signal from the local coil to the control and evaluation device. Only a few receiving antennae are required on the part of the control and evaluation device (e.g., in the patient tunnel).
One drawback of transmitting the magnetic resonance signal via a radio link is, for example, the problems of correctly orienting the transmitting antenna of the local coil (e.g., the antenna that forwards the received magnetic resonance signal to the control and evaluation device). If the transmitting antenna is not aligned, greater demands are consequently made on the quality of the transmission path. The quality of the transmission path is critical, since, otherwise, reliable transmission from the local coil to the control and evaluation device is not possible. High path losses may occur, for example, in the case of disadvantageous constellations such that, even in the case of a digital transmission, the bit error rate (BER) is so high that the radio link collapses and may not be used.
No solutions to these problems are known in practice. Various research approaches do exist, however. Reference will be made to the following:
“Wireless Local Coil Signal Transmission Using a Parametric Upconverter” by Sebastian Martius, Oliver Heid, Markus Vester, Stephan Biber and Juergen Nistler, ISMRM 2009, Poster 2934, and
“Using On-Board Microprocessors to Control a Wireless MR Receiver Array” by Matthew J. Riffe, Jeremiah A. Heilmann, Natalia Gudino and Mark A. Griswold, ISMRM 2009, Poster 2936.
Wireless video area networks (WVANs) are also known. WVANs may operate at frequencies in the range of about 60 GHz. Antenna arrays, in which the transmitting antenna is directly and automatically oriented by a search function, and a bidirectional communications protocol to the receiving antenna or the link is established via a secondary reflector in the room (e.g., by reflection on the wall), are used. Drawbacks of these methods, however, are that dedicated solutions are not available, or are only available to a limited extent, for the industrial and medical markets. Other drawbacks include that high investment expenditure is required and that bidirectional communication and control of the antenna beam in two orientations is complex.